Michael, who did not eat the brownie or have any symptoms, said he returned to the cafe the next day, bought another brownie, put it straight in the freezer and it was taken by police a week or so later.

Analysis of one brownie confirmed the presence of THC and other cannabinoids, a spokeswoman for the City of Stirling said.

She said it appeared to be an isolated incident and the city believed it had addressed any potential risk to the community.

Sharp entered his pleas in Perth Magistrates Court on Friday.

Outside court, he thanked the community for their ongoing support.

"I look forward to defending these charges," he told reporters.

"We'll let the system take its course."

In a statement issued through defence counsel Shash Nigam earlier this month, the Sharps said the family's allegations "came as a total shock".

They said they were "most disappointed" they learnt of the charges on ABC radio as they and Mr Nigam had not been served with any papers.

Sharp will face a trial allocation hearing in the same court on September 24.

The court heard the trial was expected to last more than one day and both sides would likely each call seven witnesses.